H.225 packets captured through wireshark shows that the Avaya gatekeeper rejects the Gatekeeper Request when i try to register using valid username and password.
In case when I do not provide the password, but only the username, it accepts the Gatekeeper Request, but there is no response for the Registration Request.

When connected to the AVAYA gatekeeper using Avaya one X communicator, in wireshark capture it shows that it uses password symmetric encryption or key Exchange encryption algorithms. I think Avaya one X uses an algorithm to authenticate with its gatekeeper.